Peer-to-peer name resolution protocol (PNRP) security infrastructure and method

ABSTRACT

A security infrastructure and methods are presented that inhibit the ability of a malicious node from disrupting the normal operations of a peer-to-peer network. The methods of the invention allow both secure and insecure identities to be used by nodes by making them self-verifying. When necessary or opportunistic, ID ownership is validated by piggybacking the validation on existing messages. The probability of connecting initially to a malicious node is reduced by randomly selecting to which node to connect. Further, information from malicious nodes is identified and can be disregarded by maintaining information about prior communications that will require a future response. Denial of service attacks are inhibited by allowing the node to disregard requests when its resource utilization exceeds a predetermined limit. The ability for a malicious node to remove a valid node is reduced by requiring that revocation certificates be signed by the node to be removed.

This is a divisional of U.S. application Ser. No. 10/134,780, filed Apr.29, 2002, the entire disclosure of which is incorporated herein byreference.

FIELD OF THE INVENTION

The disclosure relates generally to peer-to-peer protocols, and moreparticularly to security framework infrastructures for peer-to-peerprotocols.

BACKGROUND

Peer-to-peer (P2P) communication, and in fact all types ofcommunication, depend on the possibility of establishing validconnections between selected entities. However, entities may have one orseveral addresses that may vary because the entities move in thenetwork, because the topology changes, or because an address leasecannot be renewed. A classic architectural solution to this addressingproblem is thus to assign to each entity a stable name, and to “resolve”this name to a current address when a connection is needed. This name toaddress translation must be very robust, and it must also allow for easyand fast updates.

To increase the likelihood that an entity's address may be found bythose seeking to connect to it, many peer-to-peer protocols, includingthe Peer Name Resolution Protocol (PNRP), allow entities to publishtheir address through various mechanisms. Some protocols also allow aclient to acquire knowledge of other entities' addresses through theprocessing of requests from others in the network. Indeed, it is thisacquisition of address knowledge that enables successful operation ofpeer-to-peer networks. That is, the better the information about otherpeers in the network, the greater the likelihood that a search for aparticular resource will converge.

However, without a robust security infrastructure underlying thepeer-to-peer protocol, malicious entities can easily disrupt the abilityfor such peer-to-peer systems to converge. Such disruptions may becaused, for example, by an entity that engages in identity theft. Insuch an identity theft attack on the peer-to-peer network, a maliciousnode publishes address information for identifications (IDs) with whichit does not have an authorized relationship, i.e. it is neither theowner nor a group member, etc. A malicious entity could also interceptand/or respond first before the good node responds, thus appearing to bethe good node.

Commonly, P2P network attacks may attempt to disrupt or exhaust node ornetwork resources. In PNRP, a malicious entity could also obstruct PNRPresolution by flooding the network with bad information so that otherentities in the network would tend to forward requests to nonexistentnodes (which would adversely affect the convergence of searches), or tonodes controlled by the attacker. PNRP's name resolution ability couldalso be degraded by modifying the RESOLVE packet used to discoverresources before forwarding it to a next node, or by sending an invalidRESPONSE to back to the requester that generated the RESOLVE packet. Amalicious entity could also attempt to disrupt the operation of thepeer-to-peer network by trying to ensure that searches will not convergeby, for example, instead of forwarding the search to a node in its cachethat is closer to the ID to aid in the search convergence, forwardingthe search to a node that is further away from the requested ID.Alternatively, the malicious entity could simply not respond to thesearch request at all. The PNRP resolution could be further hampered bya malicious node sending an invalid BYE message on behalf of a valid ID.As a result, other nodes in the cloud will remove this valid ID fromtheir cache, decreasing the number of valid nodes stored therein.

While simply validating address certificates may prevent the identitytheft problem, such is ineffective against an attack that impedes PNRPresolution. An attacker can continue to generate verifiable addresscertificates (or have them pre-generated) and flood the correspondingIDs in the peer-to-peer cloud. If any of the nodes attempts to verifyownership of the ID, the attacker would be able to verify that it is theowner for the flooded IDs because, in fact, it is. However, if theattacker manages to generate enough IDs it can bring most of thepeer-to-peer searches to one of the nodes it controls. Once a maliciousnode brings the search to controlled node, the attacker fairly controlsand directs the operation of the network.

A malicious node may also attempt a denial of service (DoS) attack. Whena P2P node changes, it may publish its new information to other networknodes. If all the nodes that learn about the new node records try toperform an ID ownership check, a storm of network activity against theadvertised ID owner will occur. Exploiting this weakness, an attackercould mount an internet protocol (IP) DoS attack against a certaintarget by making that target very popular. For example, if a maliciousentity advertises an Internet Website IP address as the updated node'sID IP, all the nodes in the peer-to-peer network that receive thisadvertised IP will try to connect to that IP to verify the authenticityof the record. Of course, the Website's server will not be able toverify ownership of the ID because the attacker generated thisinformation. However, the damage has already been done. That is, theattacker convinced a good part of the peer-to-peer community to floodthe IP address with validation requests and may have effectively shut itdown.

Another type of DoS attack that overwhelms a node or a cloud byexhausting one or more resources occurs when a malicious node sends alarge volume of invalid/valid peer address certificates (PACs) to asingle node (e.g. by using FLOOD/RESOLVE/SOLICIT packets). The node thatreceives these PACs will consume all its CPU trying to verify all of thePACs. Similarly, by sending invalid FLOOD/RESOLVE packets, a maliciousnode will achieve packet multiplication within the cloud. That is, themalicious node can consume network bandwidth for a PNRP cloud using asmall number of such packets because the node to which these packets aresent will respond by sending additional packets. Network bandwidthmultiplication can also be achieved by a malicious node by sending bogusREQUEST messages to which good nodes will respond by FLOODing the PACs,which are of a larger size than the REQUEST.

A malicious node can also perpetrate an attack in the PNRP cloud byobstructing the initial node synch up. That is, to join the PNRP cloud anode tries to connect to one of the nodes already present in the PNRPcloud. If the node tries to connect to the malicious node, it can becompletely controlled by that malicious node. Further, a malicious nodecan send invalid REQUEST packets when two good nodes are involved in thesynchronization process. This is a type of DoS attack that will hamperthe synch up. Because the invalid REQUEST packets generate FLOODmessages in response, initial node synch up may be hindered.

There exists a need in the art, therefore, for security mechanisms thatwill ensure the integrity of the P2P cloud by preventing or mitigatingthe effect of such attacks.

SUMMARY

The concepts disclosed herein involve a new and improved method forinhibiting a malicious node's ability to disrupt normal operation of apeer-to-peer network. Specifically, the disclosure presents methods toaddress various types of attacks that may be launched by a maliciousnode, including identity theft attacks, denial of service attacks,attacks that merely attempt to hamper the address resolution in thepeer-to-peer network, as well as attacks that attempt to hamper a newnode's ability to join and participate in the peer-to-peer network.

The security infrastructure and methods presented allow both secure andinsecure identities to be used by nodes by making them self-verifying.When necessary or opportunistic, ID ownership is validated bypiggybacking the validation on existing messages or, if necessary, bysending a small inquire message. The probability of connecting initiallyto a malicious node is reduced by randomly selecting the connectionnode. Further, information from malicious nodes is identified and can bedisregarded by maintaining information about prior communicationsrequiring a future response. Denial of service attacks are inhibited byallowing the node to disregard requests when its resource utilizationexceeds a predetermined limit. The ability for a malicious node toremove a valid node is reduced by requiring revocation certificates tobe signed by the node to be removed.

In accordance with one embodiment, a method of generating aself-verifiable insecure peer address certificate (PAC) that willprevent a malicious node from publishing another node's secureidentification in an insecure PAC in the peer-to-peer network ispresented. This method comprises the steps of generating an insecure PACfor a resource discoverable in the peer-to-peer network. The resourcehas a peer-to-peer identification (ID). The method further includes thestep of including a uniform resource identifier (URI) in the insecurePAC from which the peer-to-peer ID is derived. Preferably, the URI is inthe format “p2p://URI”. The peer-to-peer ID may also be insecure.

In a further embodiment, a method of opportunistically validating a peeraddress certificate at a first node in a peer-to-peer network ispresented. This first node utilizes a multilevel cache for storage ofpeer address certificates, and the method comprises the steps ofreceiving a peer address certificate (PAC) purportedly from a secondnode and determining the PAC storage level in the multilevel cache. Whenthe PAC is to be stored in one of two lowest cache levels, the methodplaces the PAC in a set aside list, generates an INQUIRE messagecontaining an ID of the PAC to be validated, and transmits the INQUIREmessage to the second node. When the PAC is to be stored in an uppercache level other than one of the two lowest cache levels, the methodstores the PAC in the upper cache level marked as ‘not validated’. Inthis case, the PAC will be validated the first time it is used. Themethod may also request a certificate chain for the PAC.

In one embodiment, creating of the INQUIRE message comprises the step ofgenerating a transaction ID to be included in the INQUIRE message. Whenan AUTHORITY message is received from the second node in response to theINQUIRE message, the PAC is removed from the set aside list and isstored in one of the two lowest cache levels. If a certificate chain wasrequested, the AUTHORITY message is examined to determine if thecertificate chain is present and valid. If the AUTHORITY is present andvalid, the PAC is stored in the one of the two lowest cache levels, andif not, it is deleted. A transaction ID may also be used to ensure thatthe AUTHORITY message is in response to a prior communication.

In a further embodiment, a method of discovering a node in apeer-to-peer network in a manner that reduces the probability ofconnecting to a malicious node is presented. This method comprises thesteps of broadcasting a discovery message in the peer-to-peer networkwithout including any IDs locally registered, receiving a response froma node in the peer-to-peer network, and establishing a peeringrelationship with the node. In one embodiment, the step of receiving aresponse from a node comprises the step of receiving a response from atleast two nodes in the peer-to-peer network. In this situation, the stepof establishing a peering relationship with the node comprises the stepsof randomly selecting one of the at least two nodes and establishing apeering relationship with the randomly selected one of the at least twonodes.

In yet a further embodiment, a method of inhibiting a denial of serviceattack based on a synchronization process in a peer-to-peer network ispresented. This method comprises the steps of receiving a SOLICITmessage requesting cache synchronization from a first node containing apeer address certificate (PAC), examining the PAC to determine itsvalidity, and dropping the SOLICIT packet when the step of examining thePAC determines that the PAC is not valid. Preferably, when the step ofexamining the PAC determines that the PAC is valid, the method furthercomprises the steps of generating a nonce, encrypting the nonce with afirst node public key of the first node, generating an ADVERTISE messageincluding the encrypted nonce, and sending the ADVERTISE message to thefirst node. When a REQUEST message is received from the first node, themethod examines the REQUEST message to determine if the first node wasable to decrypt the encrypted nonce, and processes the REQUEST messagewhen the first node was able to decrypt the encrypted nonce.

Preferably, this method further comprises the steps of maintainingconnection information specifically identifying the communication withthe first node, examining the REQUEST message to ensure that it isspecifically related to the ADVERTISE message, and rejecting the REQUESTmessage when it is not specifically related to the ADVERTISE message. Inone embodiment, the step of maintaining connection informationspecifically identifying the communication with the first node comprisesthe steps of calculating a first bitpos as the hash of the nonce and thefirst node's identity, and setting a bit at the first bitpos in a bitvector. When this is done, the step of examining the REQUEST messagecomprises the steps of extracting the nonce and the first node'sidentity from the REQUEST message, calculating a second bitpos as thehash of the nonce and the first node's identity, examining the bitvector to determine if it has a bit set corresponding to the secondbitpos, and indicating that the REQUEST is not specifically related tothe ADVERTISE message when the step of examining the bit vector does notfind a bit set corresponding to the second bitpos. Alternatively, thenonce may be used directly as the bitpos. In this case, when the REQUESTis received, the bitpos corresponding to the enclosed nonce is checked.If it is set, this is a valid REQUEST and the bitpos is cleared.Otherwise, this is an invalid REQUEST or replay attack, and the REQUESTis discarded.

In yet a further embodiment, a method of inhibiting a denial of serviceattack based on a synchronization process in a peer-to-peer networkcomprises the steps of receiving a REQUEST message purportedly from afirst node, determining if the REQUEST message is in response to priorcommunication with the first node, and rejecting the REQUEST messagewhen the REQUEST message is not in response to prior communication withthe first node. Preferably, the step of determining if the REQUESTmessage is in response to prior communication comprises the steps ofextracting a nonce and an identity purportedly of the first node fromthe REQUEST message, calculating a bitpos as the hash of the nonce andthe identity, examining a bit vector to determine if it has a bit setcorresponding to the bitpos, and indicating that the REQUEST is not inresponse to prior communication with the first node when there is no bitset corresponding to the bitpos.

A method of inhibiting denial of service attacks based on node resourceconsumption in a peer-to-peer network is also presented. This methodcomprises the steps of receiving a message from a node in thepeer-to-peer network, examining current resource utilization, andrejecting processing of the message when the current resourceutilization is above a predetermined level. When a RESOLVE message isreceived, the step of rejecting processing of the message comprises thestep of sending an AUTHORITY message to the first node. This AUTHORITYmessage contains an indication that the RESOLVE message will not beprocessed because the current resource utilization too high. When aFLOOD message is received containing a peer address certificate (PAC)and the method determines that the PAC should be stored in one of twolowest cache levels, the step of rejecting processing of the messagecomprises the step of placing the PAC in a set aside list for laterprocessing. If the method determines that the PAC should be stored in acache level higher than two lowest cache levels, the step of rejectingprocessing of the message comprises the step of rejecting the FLOODmessage.

In another embodiment, a method of inhibiting denial of service attacksbased on node bandwidth consumption in a peer-to-peer network ispresented. This method comprises the steps of receiving a request forcache synchronization from a node in the peer-to-peer network, examininga metric indicating a number of cache synchronizations performed in thepast, and rejecting processing of the request for cache synchronizationwhen the number of cache synchronizations performed in the past exceedsa predetermined maximum. In a further embodiment, the method examinesthe metric to determine the number of cache synchronizations performedduring a predetermined preceding period of time. In this embodiment thestep of rejecting processing of the request comprises the step ofrejecting processing of the request for cache synchronization when thenumber of cache synchronizations performed in the preceding period oftime exceeds a predetermined maximum.

In another embodiment, a method of inhibiting a search based DoS attackin a peer-to-peer network comprises the steps of examining cache entriesof known peer address certificates to determine appropriate nodes towhich to send a resolution request, randomly selecting one of theappropriate nodes, and sending the resolution request to the randomlyselected node. In one embodiment the step of randomly selecting one ofthe appropriate nodes comprises the step of calculating a weightedprobability for each of the appropriate nodes based on the distance ofthe PNRP ID from the target ID. The probability of choosing a specificnext hop is then determined as an inverse proportionality to the IDdistance between that node and the target node.

In a further embodiment, a method of inhibiting a search based denial ofservice attack in a peer-to-peer network comprises the steps ofreceiving a RESPONSE message, determining if the RESPONSE message is inresponse to a prior RESOLVE message, and rejecting the RESPONSE messagewhen the RESPONSE message is not in response to the prior RESOLVEmessage. Preferably, the step of determining if the RESPONSE message isin response to a prior RESOLVE message comprises the steps ofcalculating a bitpos as a hash of information in the RESPONSE message,and examining a bit vector to determine if a bit corresponding to thebitpos is set therein.

In one embodiment wherein the RESPONSE message contains an address list,the method further comprises the steps of determining if the RESPONSEmessage has been modified in an attempt to hamper resolution, andrejecting the RESPONSE message when the RESPONSE message has beenmodified in an attempt to hamper resolution. Preferably the step ofdetermining if the RESPONSE message has been modified in an attempt tohamper resolution comprises the steps of calculating a bitpos as a hashof the address list in the RESPONSE message, and examining a bit vectorto determine if a bit corresponding to the bitpos is set therein.

In another embodiment, a method of inhibiting a malicious node fromremoving a valid node from the peer-to-peer network comprises the stepsof receiving a revocation certificate purportedly from the valid nodehaving a peer address certificate (PAC) stored in the receiving nodecache, and verifying that the revocation certificate is signed by thevalid node.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram generally illustrating an exemplary computersystem;

FIG. 2 is a simplified flow diagram illustrating security aspects ofAUTHORITY packet processing;

FIG. 3 is a simplified communications processing flow diagramillustrating security aspects of a synchronization phase of P2Pdiscovery;

FIG. 4 is a simplified flow diagram illustrating security aspects ofRESOLVE packet processing;

FIG. 5 is a simplified flow diagram illustrating security aspects ofFLOOD packet processing; and

FIG. 6 is a simplified flow diagram illustrating security aspects ofRESPONSE packet processing.

While the following text includes certain preferred embodiments, thereis no intent to limit it to those embodiments. On the contrary, theintent is to cover all alternatives, modifications and equivalents asincluded within the spirit and scope of the disclosure.

DETAILED DESCRIPTION

Turning to the drawings, wherein like reference numerals refer to likeelements, an exemplary system for implementing the claims includes asuitable computing environment. Although not required, the patent willbe described in the general context of computer-executable instructions,such as program modules, being executed by a personal computer.Generally, program modules include routines, programs, objects,components, data structures, etc. that perform particular tasks orimplement particular abstract data types. Moreover, those skilled in theart will appreciate that the patent may be practiced with other computersystem configurations, including hand-held devices, multi-processorsystems, microprocessor based or programmable consumer electronics,network PCs, minicomputers, mainframe computers, and the like. Thepatent may also be practiced in distributed computing environments wheretasks are performed by remote processing devices that are linked througha communications network. In a distributed computing environment,program modules may be located in both local and remote memory storagedevices.

FIG. 1 illustrates an example of a suitable computing system environment100. The computing system environment 100 is only one example of asuitable computing environment and is not intended to suggest anylimitation as to the scope of use or functionality of the patent.Neither should the computing environment 100 be interpreted as havingany dependency or requirement relating to any one or combination ofcomponents illustrated in the exemplary operating environment 100.

The patent is operational with numerous other general purpose or specialpurpose computing system environments or configurations. Examples ofwell known computing systems, environments, and/or configurations thatmay be suitable for use with the patent include, but are not limited to,personal computers, server computers, hand-held or laptop devices,multiprocessor systems, microprocessor-based systems, set top boxes,programmable consumer electronics, network PCs, minicomputers, mainframecomputers, distributed computing environments that include any of theabove systems or devices, and the like.

The patent may be described in the general context ofcomputer-executable instructions, such as program modules, beingexecuted by a computer. Generally, program modules include routines,programs, objects, components, data structures, etc. that performparticular tasks or implement particular abstract data types. The patentmay also be practiced in distributed computing environments where tasksare performed by remote processing devices that are linked through acommunications network. In a distributed computing environment, programmodules may be located in both local and remote computer storage mediaincluding memory storage devices.

With reference to FIG. 1, an exemplary system for implementing thepatent includes a general purpose computing device in the form of acomputer 110. Components of computer 110 may include, but are notlimited to, a processing unit 120, a system memory 130, and a system bus121 that couples various system components including the system memoryto the processing unit 120. The system bus 121 may be any of severaltypes of bus structures including a memory bus or memory controller, aperipheral bus, and a local bus using any of a variety of busarchitectures. By way of example, and not limitation, such architecturesinclude Industry Standard Architecture (ISA) bus, Micro ChannelArchitecture (MCA) bus, Enhanced ISA (EISA) bus, Video ElectronicsStandards Associate (VESA) local bus, and Peripheral ComponentInterconnect (PCI) bus also known as Mezzanine bus.

Computer 110 typically includes a variety of computer readable media.Computer readable media can be any available media that can be accessedby computer 110 and includes both volatile and nonvolatile media,removable and non-removable media. By way of example, and notlimitation, computer readable media may comprise computer storage mediaand communication media. Computer storage media includes both volatileand nonvolatile, removable and non-removable media implemented in anymethod or technology for storage of information such as computerreadable instructions, data structures, program modules or other data.Computer storage media includes, but is not limited to, RAM, ROM,EEPROM, flash memory or other memory technology, CD-ROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium which can be used to store the desired informationand which can be accessed by computer 110. Communication media typicallyembodies computer readable instructions, data structures, programmodules or other data in a modulated data signal such as a carrier waveor other transport mechanism and includes any information deliverymedia. The term “modulated data signal” means a signal that has one ormore of its characteristics set or changed in such a manner as to encodeinformation in the signal. By way of example, and not limitation,communication media includes wired media such as a wired network ordirect-wired connection, and wireless media such as acoustic, RF,infrared and other wireless media. Combinations of the any of the aboveshould also be included within the scope of computer readable media.

The system memory 130 includes computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) 131and random access memory (RAM) 132. A basic input/output system 133(BIOS), containing the basic routines that help to transfer informationbetween elements within computer 110, such as during start-up, istypically stored in ROM 131. RAM 132 typically contains data and/orprogram modules that are immediately accessible to and/or presentlybeing operated on by processing unit 120. By way of example, and notlimitation, FIG. 1 illustrates operating system 134, applicationprograms 135, other program modules 136, and program data 137.

The computer 110 may also include other removable/non-removable,volatile/nonvolatile computer storage media. By way of example only,FIG. 1 illustrates a hard disk drive 141 that reads from or writes tonon-removable, nonvolatile magnetic media, a magnetic disk drive 151that reads from or writes to a removable, nonvolatile magnetic disk 152,and an optical disk drive 155 that reads from or writes to a removable,nonvolatile optical disk 156 such as a CD ROM or other optical media.Other removable/non-removable, volatile/nonvolatile computer storagemedia that can be used in the exemplary operating environment include,but are not limited to, magnetic tape cassettes, flash memory cards,digital versatile disks, digital video tape, solid state RAM, solidstate ROM, and the like. The hard disk drive 141 is typically connectedto the system bus 121 through a non-removable memory interface such asinterface 140, and magnetic disk drive 151 and optical disk drive 155are typically connected to the system bus 121 by a removable memoryinterface, such as interface 150.

The drives and their associated computer storage media discussed aboveand illustrated in FIG. 1, provide storage of computer readableinstructions, data structures, program modules and other data for thecomputer 110. In FIG. 1, for example, hard disk drive 141 is illustratedas storing operating system 144, application programs 145, other programmodules 146, and program data 147. Note that these components can eitherbe the same as or different from operating system 134, applicationprograms 135, other program modules 136, and program data 137. Operatingsystem 144, application programs 145, other program modules 146, andprogram data 147 are given different numbers hereto illustrate that, ata minimum, they are different copies. A user may enter commands andinformation into the computer 110 through input devices such as akeyboard 162 and pointing device 161, commonly referred to as a mouse,trackball or touch pad. Other input devices (not shown) may include amicrophone, joystick, game pad, satellite dish, scanner, or the like.These and other input devices are often connected to the processing unit120 through a user input interface 160 that is coupled to the systembus, but may be connected by other interface and bus structures, such asa parallel port, game port or a universal serial bus (USB). A monitor191 or other type of display device is also connected to the system bus121 via an interface, such as a video interface 190. In addition to themonitor, computers may also include other peripheral output devices suchas speakers 197 and printer 196, which may be connected through a outputperipheral interface 195.

The computer 110 may operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer180. The remote computer 180 may be another personal computer, a server,a router, a network PC, a peer device or other common network node, andtypically includes many or all of the elements described above relativeto the personal computer 110, although only a memory storage device 181has been illustrated in FIG. 1. The logical connections depicted in FIG.1 include a local area network (LAN) 171 and a wide area network (WAN)173, but may also include other networks. Such networking environmentsare commonplace in offices, enterprise-wide computer networks, intranetsand the Internet.

When used in a LAN networking environment, the personal computer 110 isconnected to the LAN 171 through a network interface or adapter 170.When used in a WAN networking environment, the computer 110 typicallyincludes a modem 172 or other means for establishing communications overthe WAN 173, such as the Internet. The modem 172, which may be internalor external, may be connected to the system bus 121 via the user inputinterface 160, or other appropriate mechanism. In a networkedenvironment, program modules depicted relative to the personal computer110, or portions thereof, may be stored in the remote memory storagedevice. By way of example, and not limitation, FIG. 1 illustrates remoteapplication programs 185 as residing on memory device 181. It will beappreciated that the network connections shown are exemplary and othermeans of establishing a communications link between the computers may beused.

In the description that follows, the patent will be described withreference to acts and symbolic representations of operations that areperformed by one or more computer, unless indicated otherwise. As such,it will be understood that such acts and operations, which are at timesreferred to as being computer-executed, include the manipulation by theprocessing unit of the computer of electrical signals representing datain a structured form. This manipulation transforms the data or maintainsit at locations in the memory system of the computer, which reconfiguresor otherwise alters the operation of the computer in a manner wellunderstood by those skilled in the art. The data structures where datais maintained are physical locations of the memory that have particularproperties defined by the format of the data. However, while the patentis being described in the foregoing context, it is not meant to belimiting as those of skill in the art will appreciate that various ofthe acts and operation described hereinafter may also be implemented inhardware.

As introduced above, the success of a peer-to-peer (P2P) protocoldepends on the protocol's ability to establish valid connections betweenselected entities. Because a particular user may connect to the networkin various ways at various locations having different addresses, apreferred approach is to assign a unique identity to the user, and thenresolve that identity to a particular address through the protocol. Sucha peer-to-peer name resolution protocol (PNRP) to which the securityinfrastructure of the patent finds particular applicability is describedin co-pending application Ser. No. 09/942,164, entitled Peer-To-PeerName Resolution Protocol (PNRP) And Multilevel Cache For Use Therewith,filed on Aug. 29, 2001, the teachings and disclosure of which are herebyincorporated in their entireties by reference thereto. However, oneskilled in the art will recognize from the following teachings that thesecurity infrastructure and methods are not limited to the particularpeer-to-peer protocol of this co-pending application, but may be appliedto other protocols with equal force.

As discussed in the above-incorporated co-pending application, the peername resolution protocol (PNRP) is a peer-based name-to-addressresolution protocol. Names are 256-bit numbers called PNRP IDs.Addresses consist of an IPv4 or IPv6 address, a port, and a protocolnumber. When a PNRP ID is resolved into an address, a peer addresscertificate (PAC) is returned. This certificate includes the target'sPNRP ID, current IP address, public key, and many other fields. Aninstance of the PNRP protocol is called a node. A node may have one ormore PNRP IDs registered locally. A node makes an ID-to-address mappingdiscoverable in PNRP via registration. Each registration includes alocally constructed peer certificate, and requires an appropriate viewof the PNRP cache. Hosts which are not PNRP nodes may resolve PNRP IDsinto IP addresses via a PNRP DNS gateway. A PNRP DNS gateway accepts DNS‘A’ and ‘AAAA’ queries, performs a PNRP search for a subset of thehostname specified, and returns the results as a DNS query answer.

As indicated above, PNRP provides a peer-based mechanism associating P2Pand PNRP IDs with peer address certificates (PACs). A P2P ID is apersistent 128-bit identifier. P2P IDs are created by hashing acorrectly formatted P2P name. There are two types of P2P IDs, secure andinsecure. A secure P2P ID is an ID with a verifiable relationship to apublic key. An insecure P2P ID is any ID which is not secure. A givenP2P ID may be published by many different nodes. PNRP uses a ‘servicelocation’ suffix to ensure each published instance has a unique PNRP ID.A ‘service location’ is a 128-bit number corresponding to a uniquenetwork service endpoint. Service locations have some recognizableelements, but should be considered opaque by PNRP clients. A servicelocation has two important properties. At any moment, only one socket inthe cloud corresponds to a given service location. When two servicelocations are compared, the length of the common prefix for each is areasonable measure of network proximity. Two service locations whichstart with the same four bits are no further apart than two which startwith the same three bits.

A P2P ID is uniquely identified by its catenation with the servicelocation. The resulting 256-bit (32 byte) identifier is called a PNRPID. PNRP nodes register a PNRP ID by invoking PNRP services with a P2Pname, authority, and several other parameters. PNRP services thencreates and maintains a Peer Address Certificate (PAC) containing thesubmitted data. PACs include at a minimum a PNRP ID, certificatevalidity interval, service and PNRP address, public key, and acryptographic signature generated over select PAC contents.

Creation and registration of PNRP IDs is only one part of the PNRPservice. The PNRP service execution can be divided into four phases. Thefirst is PNRP cloud discovery. During this phase a new node must find anexisting node in the cloud it wishes to join. The cloud may be theglobal PNRP cloud, a site local (enterprise) cloud, or a link localcloud. Once found, the second phase of joining a PNRP cloud is entered.Once the new node has found an existing node, it performs a SYNCHRONIZEprocedure to obtain a copy of the existing node's top cache level. Asingle cache level provides enough basis for a new node to startparticipating in the cloud. Once the SYNCHRONIZATION has been achieved,the next phase, active participation in the cloud, may be begun. Afterinitialization has completed, the node may participate in PNRP IDregistration and resolution. During this phase, the peer also performsregular cache maintenance. When the node is done, it enters the fourthphase, leaving the cloud. The node un-registers any locally registeredPNRP IDs, then terminates.

The PNRP protocol consists of nine different types of packets, some ofwhich have been introduced above. It should be noted, however, that inthis application the names of the packets are used merely to facilitatean understanding of their functionality, and should not be taken aslimiting the form or format of the packet or message itself. The RESOLVEpacket requests resolution of a target PNRP ID into a PAC. A RESPONSEpacket is the result of a completed RESOLVE request. The FLOOD packetcontains a PAC intended for the PNRP cache of the recipient. A SOLICITpacket is used to ask a PNRP node to ADVERTISE its top level cache. Therequested ADVERTISE packet contains a list of PNRP IDs for PACs in anode's top level cache. A REQUEST packet is used to ask a node to flooda subset of ADVERTISE'd PACs. An INQUIRE packet is used to insecurelyask a node whether a specific PNRP ID is registered at that node. Toconfirm local registration of a PNRP ID, an AUTHORITY packet is used.This packet optionally provides a certification chain to help validatethe PAC for that ID. An ACK packet acknowledges receipt and/orsuccessful processing of certain messages. Finally, the REPAIR packet isused to try to merge clouds that may be split.

Once a node is fully initialized, it may participate in the PNRP cloudby performing five types of activities. First, a node may register andun-register PNRP IDs. When a PNRP ID is registered, the PNRP servicecreates a peer address certificate (PAC) associating the PNRP ID,service address port and protocol, PNRP address port and protocol, and apublic key. This PAC is entered into the local cache, and a RESOLVE isinitiated using the new PAC as the source, and [PNRP ID+1] as thetarget. This RESOLVE is processed by a number of nodes with PNRP IDsvery similar to the registered ID. Each recipient of the RESOLVE addsthe new node's PAC to their cache, thereby advertising the new PNRP IDin the cloud. When a PNRP ID is un-registered, an updated PAC is createdwith a ‘revoke’ flag set. The updated PAC is flooded to all entries inthe lowest level of the local cache. Each recipient of the FLOOD checksits cache for an older version of the PAC. If one is found, therecipient removes the PAC from its cache. If the PAC is removed from thelowest cache level, the recipient in turn FLOODs the revocation to thePNRP nodes represented by all other PACs in its lowest cache level.

The PNRP node may also participate in PNRP ID resolution. As discussedin the above incorporated application, PNRP IDs are resolved into PACsby routing RESOLVE messages successively closer to the target PNRP ID.When a node receives a RESOLVE, it may reject the RESOLVE back to theprevious hop, respond to the previous hop with a RESPONSE, or forwardthe RESOLVE to a node whose PNRP ID is closer to the target ID than thenode's own. The node also receives and forwards RESPONSE packets as partof resolution. The PNRP node may also initiate RESOLVEs on behalf of alocal client. The PNRP service provides an API to allow asynchronousresolution requests. The local node originates RESOLVE packets, andeventually receives a corresponding RESPONSE.

The PNRP node also honors cache synchronization requests. Upon receivinga SOLICIT packet, the node responds with an ADVERTISE packet, listingthe PNRP IDs in its highest cache level. The solicitor node then sends aREQUEST listing the PNRP IDs for any ADVERTISE'd PACs it wants. EachREQUESTed cache entry is then FLOODed to the REQUESTor. Finally, and aswill be discussed more fully below, the PNRP also performs identityvalidation. Identity validation is a threat mitigation device used tovalidate PACs. Identity validation basically has two purposes. First,identity validation ensures that the PNRP node specified in a PAC hasthe PNRP ID from that PAC locally registered. Second, for secure PNRPIDs (discussed below), identity validation ensures that the PAC wassigned using a key with a cryptographically provable relationship to theauthority in the PNRP ID.

Having now provided a working knowledge of the PNRP system for which anembodiment of the security infrastructure finds particular relevance,attention is now turned to the security mechanisms provided by thesecurity infrastructure. These mechanisms are provided to eliminate, orat a minimum mitigate, the effect of the various attacks that may beposed by a malicious node in a P2P cloud as discussed above. The PNRPprotocol does not have any mechanism to prevent these attacks, nor isthere a single solution to address all of these threats. The securityinfrastructure, however, minimizes the disruption that may be caused bya malicious node, and may be incorporated into the PNRP protocol.

As with many successful P2P protocols, entities can be published foreasy discovery. To provide security and integrity to the P2P protocol,however, each identity preferably includes an attached identitycertificate. However, a robust security architecture will be able tohandle both secure and insecure entities. This robustness is providedthrough the use of self-verifying PACs.

A secure PAC is made self-verifying by providing a mapping between theID and a public key. This will prevent anyone from publishing a securePAC without having the private key to sign that PAC, and thus willprevent a large number of identity theft attacks. The keeper of the IDprivate key uses the certificate to attach additional information to theID, such as the IP address, friendly name, etc. Preferably, each nodegenerates its own pair of private-public keys, although such may beprovided by a trusted supplier. The public key is then included as partof the node identifier. Only the node that created the pair of keys hasthe private key with which it can prove that it is the creator of thenode identity. In this way, identity theft may be discovered, and is,therefore, deterred.

A generic format for such certificates may be represented as [Version,ID, <ID Related Info>, Validity, Algorithms, P.sub.Issuer]K.sub.Issuer.Indeed, P2P name/URL is part of the basic certificate format, regardlessof whether it is a secure or insecure ID. As used in this certificaterepresentation, Version is the certificate version, ID is the identifierto be published, <ID Related Info> represents information to beassociated with the ID, Validity represents the period of validityexpressed in a pair of From-To dates expressed as Universal Date Time(aka GMT), Algorithms refers to the algorithms used for generating thekey pairs, and for signing, and P.sub.Issuer is the public key of thecertificate issuer. If the certificate issuer is the same as the IDowner then this is P.sub.ID the public key of the ID owner. The termK.sub.Issuer is the private key corresponding to P.sub.Issuer. If thecertificate issuer is the ID owner then this is K.sub.ID, the privatekey of the ID owner.

In a preferred embodiment, the <ID related info> comprises the addresstuple where this ID can be found, and the address tuple for the PNRPservice of the issuer. In this embodiment, the address certificatebecomes [Version, ID, <Address>.sub.ID, <Address>.sub.PNRP, Validity,Revoke Flag, Algorithms, P.sub.Issuer]K.sub.Issuer. In this expandedrepresentation, the ID is the identifier to be published, which can be aGroup ID or Peer ID. The <Address> is the tuple of IPv6 address, port,and protocol. <Address>.sub.ID is the address tuple to be associatedwith the ID. <Address>.sub.PNRP is the address tuple of the PNRP service(or other P2P service) on the issuer machine. This is preferably theaddress of the PNRP address of the issuer and will be used by the otherPNRP nodes to verify the validity of the certificate. Validity is theperiod of validity expressed in a pair of From-To dates. The RevokeFlag, when set, marks a revocation certificate. The P.sub.Issuer is thepublic key of the certificate issuer, and the K.sub.Issuer is theprivate key corresponding to P.sub.Issuer. If the certificate issuer isthe ID owner then this is K.sub.ID, the private key of the ID.

In one embodiment, the following conditions have to be met for acertificate to be valid. The certificate signature must valid, and thecertificate cannot be expired. That is, the current date expressed asUDT must be in the range specified by the Validity field. The hash ofthe public key must also match the ID. If the Issuer is the same as theID owner then the hashing of the issuer's public key into the ID has toverify. If the P.sub.Issuer is different from P.sub.ID then there mustbe a chain of certificates leading to a certificate signed withK.sub.ID. Such a chain verifies the relationship between the issuer andthe ID owner. Additionally, in the case when a certification revocationlist (CRL) is published for that class of IDs and the CRL is accessible,then the authenticator can verify that none of the certificates in thechain appear in the CRL.

The security infrastructure also handles insecure PACs. An insecure PACis made self-verifying by including the uniform resource identifier(URI) from which the ID is derived. Indeed, both secure and insecure IDsinclude the URI in the PAC. The URI is of the format “p2p://URI”. Thiswill prevent a malicious node from publishing another node's secure IDin an insecure PAC.

The security infrastructure also allows for the use of insecure IDs. Theproblem with insecure IDs is that they are very easy to forge: amalicious node can publish an insecure ID of any other node. InsecureIDs also open security holes wherein it becomes possible to makediscovery of a good node difficult. However, by including a URI, theinsecure IDs cannot affect the secure IDs in any way. Further, theinfrastructure requires that the PACs containing insecure IDs be in thesame format as secure PACs, i.e. they contain public key and privatekeys. By enforcing the same structure on both insecure PACs and securePACs, the bar for generating PACs is not lowered. Further, by includinga URI in the PAC it is not computationally feasible to generate a URIthat maps to a specific secure ID.

One issue that arises is the timing of PAC verification, recognizing atrade off between increased P2P cloud security and increased overhead.The PAC contained in the various packets discussed above has to beverified at some point, however. This PAC verification includes checkingthe ID signature validity and checking if the ID corresponds to thepublic key for secure IDs. To balance the overhead versus securityissues, one embodiment verifies the PACs before any processing of thatpacket is done. This ensures that invalid data is never processed.However, recognizing that PAC verification may slow down the packetprocessing, which might not be suitable for certain classes of packets(e.g. RESOLVE packets), an alternate embodiment does not verify the PACin these packets.

In addition to PAC verification, the security also performs an IDownership check to validate the PAC. As discussed above, identity theftcan be discovered by simple validation of the address certificate beforeusing that address in PNRP or other P2P protocols. This validation mayentail simply verifying that the ID is the hash of the public keyincluded in the certificate. The ownership validation may also entailthe issuance of an INQUIRE packet to the address in that PAC. TheINQUIRE packet will contain the ID to be verified, and a transaction ID.If the ID is present at that address, the node should acknowledge thatINQUIRE. If the ID is not present at that address, the node should notacknowledge that INQUIRE. If the certificate chain is required to verifythe identity, the node returns the complete certificate chain. Whilesignature and ID->URL validation is still complex and a significant useof resources, as is validating the chain of trust in a supplied certchain, the system avoids any sort of challenge/response protocol, whichwould add an additional level of complexity to PAC validation. Further,the inclusion of the transaction ID prevents the malicious node frompre-generating the response to the INQUIREs. Additionally, thismechanism dispenses with the requirement that the PAC carry the completecertificate chain.

The ID ownership check is also facilitated in the system by modifyingthe standard RESOLVE packet so that it can also perform the ID ownershipcheck. This modified RESOLVE packet contains the ID of the address towhich the RESOLVE is being forwarded. If the ID is at that address, itwill send an ACK, otherwise it will send a NACK. If the ID does notprocess the RESOLVE or if a NACK is received, the ID is removed from thecache. In this way a PAC is validated without resorting to any sort ofchallenge/response protocol and without sending any special INQUIREpacket by, in essence, piggybacking an INQUIRE message with the RESOLVE.This piggybacking process will be discussed again below with respect toFIG. 2. This procedure makes it easy to flush out invalid or stale PACs.

This identity validation check happens at two different times. The firstis when a node adds a PAC to one of its lowest two cache levels. PACvalidity in the lowest two cache levels is critical to PNRP's ability toresolve PNRP IDs. Performing identity validation before adding a PAC toeither of these two levels mitigates several attacks. ID ownership isnot performed if the PAC is added to any higher level cache because ofthe turnover in these higher levels. It has been determined that nearly85% of all PAC entries in the higher levels of cache are replaced orexpire before they are ever used. As such, the probability of seeing anyeffect from having an invalid PAC in these higher levels is low enoughnot to justify performing the ID validation when they are entered.

When it is determined that an entry would belong in one of the twolowest cache levels, the PAC is placed in a set aside list until itsidentity can be validated. This first type of identity validation usesthe INQUIRE message. Such an identity validation confirms a PAC is stillvalid (registered) at its originating node, and requests information tohelp validate authority of the originating node to publish that PAC. Oneflag in the INQUIRE message is defined for the ‘flags’ field, i.e.RF_SEND_CHAIN, that requests the receiver to send a certificate chain(if any exists) in an AUTHORITY response. If the receiver of the INQUIREdoes not have authority to publish the PAC or if the PAC is no longerlocally registered, the receiver simply drops the INQUIRE message. Sincethe local node does not receive a proper response via an AUTHORITYmessage, the bad PAC will never be entered into its cache, and thereforecan have no malicious effect on its operation in the P2P cloud.

If the receiver of the INQUIRE does have the authority to issue the PACand if it is still locally registered, that node will respond 200 to theINQUIRE message with an AUTHORITY message as illustrated in FIG. 2.While not illustrated in FIG. 2, the receiving node in an embodimentchecks to see if the AUTHORITY message says that the ID is stillregistered at the node which sent the AUTHORITY. Once the local nodedetermines 202 that this AUTHORITY message is in response to the INQUIREmessage, it removes the PAC from the set aside list 204. If thecertificate chain was requested 206, the AUTHORITY message is checked tosee if the certificate chain is present and valid 208. If thecertificate chain is present and valid, then the PAC is added to thecache and marked as valid 210. Otherwise, the PAC is deleted 212. If thecertificate chain was not requested 206, then the PAC is simply added tothe cache and marked as valid 210.

As may now be apparent, this AUTHORITY message is used to confirm ordeny that a PNRP ID is still registered at the local node, andoptionally provides a certificate chain to allow the AUTHORITY recipientto validate the node's right to publish the PAC corresponding to thetarget ID. In addition to the INQUIRE message, the AUTHORITY message maybe a proper response to a RESOLVE message as will be discussed below.The AUTHORITY message includes various flags that may be set by thereceiving node to indicate a negative response. One such flag is theAF_REJECT_TOO_BUSY flag, which is only valid in response to a RESOLVE.This flag indicates that the host is too busy to accept a RESOLVE, andtells the sender that it should forward the RESOLVE elsewhere forprocessing. While not aiding in the identity validation, it is anothersecurity mechanism to prevent a DoS attack as will be discussed morefully below. The flag AF_INVALID_SOURCE, which is only valid in responseto a RESOLVE, indicates that the Source PAC in the RESOLVE is invalid.The AF_INVALID_BEST_MATCH flag, which is also only valid in response toa RESOLVE, indicates that the ‘best match’ PAC in the RESOLVE isinvalid. The AF_UNKNOWN_ID flag indicates that the specified ‘validate’PNRP ID is not registered at this host. Other flags in the AUTHORITYmessage indicate to the receiving node that requested information isincluded. The AF_CERT_CHAIN flag indicates that a certificate chain isincluded that will enable validation of the relationship between the‘validate’ PNRP ID and the public key used to sign the PAC. TheAUTHORITY message is only sent as an acknowledgement/response to eitherthe INQUIRE or RESOLVE messages. If an AUTHORITY is ever received out ofthis context, it is discarded.

The second time that identity validation is performed isopportunistically during the RESOLVE process. As discussed, PNRP cacheshave a high rate of turnover. Consequently, most cache entries areoverwritten in the cache before they are ever used. Therefore, thesecurity infrastructure does not validate these PACs until and unlessthey are actually used. When a PAC is used to route a RESOLVE path, thesystem piggybacks identity validation on top of the RESOLVE packet asintroduced above. The RESOLVE contains a ‘next hop’ ID which is treatedthe same as the target ID in an INQUIRE packet. This RESOLVE is thenacknowledged with an AUTHORITY packet, the same as is expected for anINQUIRE discussed above. If an opportunistic identity validation fails,the receiver of the RESOLVE is not who the sender believes they are.Consequently, the RESOLVE is routed elsewhere and the invalid PAC isremoved from the cache.

This process is also illustrated in FIG. 2. When a PNRP node P receivesan AUTHORITY packet 200 with the header Message Type field set toRESOLVE 202, the receiving node examines the AUTHORITY flags todetermine if this AUTHORITY flag is negative 214, as discussed above. Ifany of the negative response flags are set in the AUTHORITY message, thePAC is deleted 216 from the cache and the RESOLVE is routed elsewhere.The address to which the RESOLVE was sent is appended to the RESOLVEpath and marked REJECTED. The RESOLVE is then forwarded to a newdestination. If the AUTHORITY is not negative and if the certificatechain was requested 218, the AUTHORITY message flag AF_CERT_CHAIN ischecked to see if the certificate chain is present. If it is present thereceiving node should perform a chain validation operation on the cachedPAC for the PNRP ID specified in validate. The chain should be checkedto ensure all certificates in it are valid, and the relationship betweenthe root and leaf of the chain is valid. The hash of the public key forthe chain root should, at a minimum, be compared to the authority in thePACs P2P name to ensure they match. The public key for the chain leafshould be compared against the key used to sign the PAC to ensure theymatch. If any of these checks fail or if the certificate chain is notpresent when requested 220, the PAC should be removed from the cache 222and the RESOLVE reprocessed. If the requested certificate chain isincluded and is validated 220, the PAC corresponding to the validatePNRP ID should be marked as fully validated 224. If desired, the PNRPID, PNRP service address, and validation times may be retained from thePAC and the PAC itself deleted from the cache to save memory.

As an example of this identity validation, assume that ‘P’ is a noderequesting an identity validation for PNRP ID ‘T’. ‘N’ is the nodereceiving the identity validation request. This could happen as a resultof P receiving either an INQUIRE packet with target ID=T, or a RESOLVEpacket with next hop=T. N checks its list of PNRP IDs registeredlocally. If T is not in that list, then the received packet type ischecked. If it was an INQUIRE, N silently drops the INQUIRE request.After normal retransmission attempts expire, P will discard the PAC asinvalid and processing is done. If it was a RESOLVE, N responds with anAUTHORITY packet indicating ID T is not locally registered. P then sendsthe RESOLVE elsewhere. If T is in the list of PNRP IDs at N, Nconstructs an AUTHORITY packet and sets the target ID to T. If T is aninsecure ID, then N sends the AUTHORITY packet to P. If T is a secureID, and the authority for the secure ID is the key used to sign the PAC,then N sends the AUTHORITY packet to P. If neither of these are true andif the RF_SEND_CHAIN flag is set, then N retrieves the certificate chainrelating the key used to sign the PAC to the authority for PNRP ID T.The certificate chain is inserted into the AUTHORITY packet, and then Nsends the AUTHORITY packet to P. At this point, if T is an insecure IDprocessing is completed. Otherwise, P validates the relationship betweenthe PAC signing key and the authority used to generate the PNRP ID T. Ifthe validation fails, the PAC is discarded. If validation fails and theinitiating message was a RESOLVE, P forwards the RESOLVE elsewhere.

As may now be apparent from these two times that identity ownershipverification is performed, through either the INQUIRE or the modifiedRESOLVE packet, an invalid PAC cannot be populated throughout the P2Pcloud using a FLOOD, and searches will not be forwarded to non-existentor invalid IDs. The PAC validation is necessary for FLOOD because, ifthe FLOOD packet is allowed to propagate in the network without anyvalidation, then a DoS attack may result. Through these mechanisms, apopular node will not be flooded with ID ownership check because its IDwill belong to only a very few nodes' lowest two cache levels.

As described more fully in the above referenced co-pending application,a PNRP node N learns about a new ID in one of four ways. It may learn ofa new ID through the initial flooding of a neighbor's cache.Specifically, when a P2P node comes up it contacts another node memberof the P2P cloud and initiates a cache synchronization sequence. It mayalso learn of a new ID as a result of a neighbor flooding a new recordof its lowest cache. For example, assume that node N appears as an entryin the lowest level cache of node M. When M learns about a new ID, ifthe ID fits in its lowest level cache, it will flood it to the otherentries in that cache level, respectively to N. A node may also learn ofa new ID as a result of a search request. The originator of a searchrequest inserts its address certificate in the request, and the PAC forthe ‘best match’ to the search request so far also inserts its PAC intothe request. In this way, all of the nodes along the search request pathwill update their cache with the search originator's address, and thebest match's address. Similarly, a node may learn of a new ID as aresult of a search response. The result of a search request travels asubset of the request path in reverse order. The nodes along this pathupdate their cache with the search result.

According to PNRP, when the node first comes up it discovers a neighbor.As discussed above, however, if the node that is first discovered is amalicious node, the new node can be controlled by the malicious node. Toprevent or minimize the possibility of such occurrence, the securityinfrastructure provides two mechanisms to ensure secure node boot up.The first is randomized discovery. When a node tries to discover anothernode that will allow it to join the PNRP cloud, the last choice fordiscovery is using multicast/broadcast because it is the most insecurediscovery method of PNRP. Due to the nature of discovery it is verydifficult to distinguish between a good and bad node. Therefore, whenthis multicast/broadcast method is required, the security infrastructurecauses the node to randomly select one of the nodes who responded to thebroadcast discovery message (MARCOPOLO or an existing multicastdiscovery protocol e.g., SSDP). By selecting a random node, the systemminimizes the probability of selecting a malicious node. The system alsoperforms this discovery without using any of its IDs. By not using IDsduring discovery, the system prevents the malicious node from targetinga specific ID.

A second secure node boot up mechanism is provided by a modified syncphase during which the node will maintain a bit vector. This modifiedsynch phase mechanism may best be understood through an exampleillustrated in the simplified flow diagram of FIG. 3. Assume that Alice226 sends a SOLICIT 228 to Bob 230 with her PAC in it. If Alice's PAC isnot valid 232, Bob 230 simply drops the SOLICIT 234. If the PAC isvalid, Bob 230 will then maintain a bit vector for storing the state ofthis connection. When this SOLICIT is received, Bob 230 generates 236 anonce and hashes it with Alice's PNRP ID. The resulting number will beused as an index in this bit vector that Bob will set. Bob 230 thenresponds 238 to Alice 226 with an ADVERTISE message. This ADVERTISE willcontain Bob's PAC and a nonce encrypted with Alice's public key, apartfrom other information, and will be signed by Bob 230. When Alice 226receives this ADVERTISE, she verifies 240 the signature and Bob's PAC.If it cannot be verified, it is dropped 241. If it can be verified,Alice 226 then decrypts 242 the nonce. Alice 226 will then generate 244a REQUEST that will contain this nonce and Alice's PNRP ID. Bob 230 willprocess 246 this REQUEST by hashing Alice's PNRP ID with the nonce sentin the REQUEST packet. If 248 the bit is set in the bit vector havingthe hashed results as an index, then Bob will clear the bits and startprocessing the REQUEST 250. Otherwise, Bob will ignore the REQUEST 252as it may be a replay attack.

This makes the node boot up a secure process because the sequence cannotbe replayed. It requires minimal overhead in terms of resourcesconsumed, including CPU, network ports, and network traffic. No timersare required to be maintained for the state information, and only the IDthat initiated the sync up will be sent data. Indeed, this modified syncphase is asynchronous, which allows a node to process multiple SOLICITssimultaneously.

Many of the threats discussed above can be minimized by controlling therate at which the packets are processed, i.e. limiting node resourceconsumption. The idea behind this is that a node should not consume 100%of its CPU trying to process the PNRP packets. Therefore, in accordancewith an embodiment a node may reject processing of certain messages whenit senses that such processing will hinder its ability to functioneffectively.

One such message that the node may decide not to process is the RESOLVEmessage received from another node. This process is illustrated insimplified form in FIG. 4. Once a RESOLVE message is received 254, thenode will check 256 to see if it is currently operating at a CPUcapacity greater than a predetermined limit. If its CPU is too busy toprocess the RESOLVE message, it will send 258 an AUTHORITY message withthe AF_REJECT_TOO_BUSY flag set indicating its failure to process therequest because it is too busy. If the CPU is not too busy 256, the nodewill determine 260 if all of the PACs in the RESOLVE message are valid,and will reject 262 the message if any are found to be invalid. If allof the PACs are valid 260, the node will process 264 the RESOLVE.

If the node can respond 266 to the RESOLVE, the node will 268 convertthe RESOLVE into a RESPONSE and send it to the node from which itreceived the RESOLVE. If, however, the target ID is not locallyregistered, the node will 270 calculate the bitpos as the hash of thefields in the RESOLVE and will set the corresponding bitpos in the bitvector. As discussed briefly above, this bit vector is used as asecurity mechanism to prevent the processing of erroneous reply messageswhen the node has not sent out any messages to which a reply isexpected. The node finds the next hop to which to forward the RESOLVE,with the appropriate modifications to evidence its processing of themessage. If 272 the node to which the RESOLVE is to be forwarded hasalready been verified, the node simply forwards 276 the RESOLVE to thatnext hop. If 272 this selected next hop has not yet been verified, thenode piggybacks 274 an ID ownership request on the RESOLVE and forwards276 it to that node. In response to the piggybacked ID ownershiprequest, the node will expect to receive an AUTHORITY message asdiscussed above, the process for which is illustrated in FIG. 2. Asillustrated in FIG. 2, if a validating AUTHORITY is not received at step214, the PAC of the node to which the RESOLVE was forwarded is deleted216 from the cache and the RESOLVE is reprocessed from step 254 of FIG.4.

Another message that the node may decide not to process because its CPUis too busy is the FLOOD message. In this process, illustrated insimplified form in FIG. 5, if 278 the new information present in theFLOOD goes to either of the lowest two cache levels, the PAC is checkedto determine if it is valid 280. If the PAC is not valid, the FLOOD isrejected 284. However, if the PAC is valid 280, it is put into aset-aside list 282. The entries in the set-aside list are taken atrandom intervals and are processed when the CPU is not too busy. Sincethese entries are going to be entered in the lowest two levels of cache,both the ID verification and the ownership validation are performed asdiscussed above. If 278 the new information present in the FLOOD goes tothe higher cache levels and the CPU is too busy to process them 286,then they are discarded 288. If the node has available CPU processingcapacity 286, the PAC is checked to determine if it is valid 290. If itis, then the PAC is added to the cache 292, otherwise the FLOOD isrejected 294.

Node boot up (SYNCHRONIZE) is another process that consumes considerableresources at a node, including not only CPU processing capacity but alsonetwork bandwidth. However, the synchronization process is required toallow a new node to fully participate in the P2P cloud. As such, thenode will respond to the request from another node for the boot up if ithas enough available resources at the given time. That is, as with thetwo messages just discussed, the node may refuse to participate in theboot up if its CPU utilization is too high. However, since this processconsumes so much capacity, a malicious node can still exploit this bylaunching a large number of such sequences. As such, an embodiment ofthe security infrastructure limits the number of node synchronizationsthat may be performed by a given node to prevent this attack. Thislimitation may additionally be time limited so that a malicious nodecannot disable a node from ever performing such a synchronization againin the future.

Also discussed above were many search based attacks that could belaunched or caused by a malicious node. To eliminate or minimize theeffect of such search based attacks, the system provides two mechanisms.The first is randomization. That is, when a node is searching for anappropriate next hop to which to forward a search request (RESOLVE), itidentifies a number of possible candidate nodes and then randomlyselects one ID out of these candidate IDs to which to forward theRESOLVE. In one embodiment, three candidate nodes are identified for therandom selection. The IDs may be selected based on a weightedprobability as an alternative to total randomization. One such method ofcalculating a weighted probability that the ID belongs to anon-malicious node is based on the distance of the PNRP ID from thetarget ID. The probability is then determined as an inverseproportionality to the ID distance between that node and the targetnode. In any event, this randomization will decrease the probability ofsending the RESOLVE request to a malicious node.

The second security mechanism that is effective against search basedattacks utilizes the bit vector discussed above to maintain stateinformation. That is, a node maintains information identifying all ofthe RESOLVE messages that it has processed for which a response has notyet been received. The fields that are used to maintain the stateinformation are the target ID and the address list in the RESOLVEpacket. This second field is used to ensure that the address list hasnot been modified by a malicious node in an attempt to disrupt thesearch. As discussed above with the other instances of bit vector use,the node generates a hash of these fields from the RESOLVE and sets thecorresponding bitpos in the bit vector to maintain a history of theprocessing of that RESOLVE.

As illustrated in the simplified flow diagram of FIG. 6, when a RESPONSEmessage is received 296 from another node, the fields in this RESPONSEmessage are hashed 298 to calculate the bitpos. The node then checks 300the bit vector to see if the bitpos is set. If the bit is not set,meaning that this RESPONSE is not related to an earlier processedRESOLVE, then the packet is discarded 302. If the bitpos is set, meaningthat this RESPONSE is related to an earlier processed RESOLVE, thebitpos is reset 304. By resetting the bitpos, the node will ignorefurther identical RESPONSE messages that may be sent as part of aplayback attack from a malicious node. The node then checks to make surethat all of the PACs in the RESPONSE message are valid 306 beforeprocessing the RESPONSE and forwarding it to the next hop. If any of thePACs are invalid 306, then the node will reject 310 the packet.

The RESOLVE process mentions converting a RESOLVE request into aRESPONSE. This RESPONSE handling just discussed involves ensuring theRESPONSE corresponds to a recently received RESOLVE, and forwarding theRESPONSE on to the next hop specified. As an example, assume that node Preceives a RESPONSE packet S containing a target PNRP ID, a BestMatchPAC, and a path listing the address of all nodes which processed theoriginal RESOLVE before this node, ending with this node's own PNRPaddress. Node P acknowledges receipt of the RESPONSE with an ACK. Node Pchecks the RESPONSE path for its own address. Its address must be thelast entry in the address list for this packet to be valid. Node P alsochecks its received bit vector to ensure that the RESPONSE matches arecently seen RESOLVE. If the RESPONSE does not match a field in thereceived bit vector, or if P's address is not the last address in thepath list, the RESPONSE is silently dropped, and processing stops. Pvalidates the BestMatch PAC and adds it to its local cache. If theBestMatch is invalid, the RESPONSE is silently dropped, and processingstops. P removes its address from the end of the RESPONSE path. Itcontinues removing entries from the end of the RESPONSE path until theendmost entry has a flag set indicating a node that ACCEPTED thecorresponding RESOLVE request. If the path is now empty, thecorresponding RESOLVE originated locally. PNRP does an identityvalidation check on the BestMatch. If the identity validation checksucceeds, the BestMatch is passed up to the request manager, else afailure indication is passed up. If the path is empty, processing iscomplete. If the path is not empty, the node forwards the RESPONSEpacket to the endmost entry in the path list.

A need for a PNRP address certificate revocation exists whenever thepublished address certificate becomes invalid prior to the certificateexpiration date (Validity/To field). Examples of such events are when anode is gracefully disconnecting from the P2P network, or when a node isleaving a group, etc. The revocation mechanism utilizes the publishingof a revocation certificate. A revocation certificate has the RevokeFlag set, and the From date of the Validity field set to the currenttime (or the time at which the certificate is to become revoked) and theTo field set to the same value as the previously advertisedcertificates. All the certificates for which all the followingconditions are met are considered to be revoked: the certificate issigned by the same issuer; the ID matches the ID in the revocationcertificate; the Address fields match the ones in the revocationcertificate; the To date of the Validation field is the same as the Todate of the Validation filed in the revocation certificate; and the Fromdate of the Validation field precedes the From date of the Validationfiled in the revocation certificate. Since the revocation certificate issigned, it ensures that a malicious node cannot disconnect anyone fromthe cloud.

The foregoing description of various embodiments has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the embodiments disclosed. Numerous modificationsor variations are possible in light of the above teachings. Theembodiments discussed were chosen and described to provide the bestillustration of the disclosed principles and its practical applicationto thereby enable one of ordinary skill in the art to utilize theembodiments with various modifications as are suited to the particularuse contemplated. All such modifications and variations are within thescope of the disclosure as determined by the appended claims wheninterpreted in accordance with the breadth to which they are fairly,legally, and equitably entitled.

1. A method of inhibiting denial of service attacks based on consumptionof processor capacity at a node in a peer-to-peer network, comprising:receiving a potentially malicious message at the node in thepeer-to-peer network; wherein the potentially malicious messagecomprises a RESOLVE message, the RESOLVE message comprising at least onemessage field; examining processor capacity at the node; and rejectingprocessing of the potentially malicious RESOLVE message when examiningthe processor capacity at the node indicates that the consumption ofprocessor capacity at the node is above a predetermined level, whereinrejecting processing of the potentially malicious RESOLVE messagecomprises sending an AUTHORITY message, the AUTHORITY message containingan indication that the potentially malicious RESOLVE message will not beprocessed because the consumption of processor capacity at the node isabove the predetermined level; and accepting processing of the RESOLVEmessage when examining the node processor capacity indicates that theconsumption of processor capacity at the node is below the predeterminedlevel, and processing the RESOLVE message at the node.
 2. The method ofclaim 1, further comprising: calculating a bitpos as a hash of the atleast one message field when a first node identification is not locallyregistered; setting a first bit at an index of a bit vector, the indexof the bit vector corresponding to the bitpos; storing the bit vector atthe node, the bit vector specifically identifying the RESOLVE messagewith a sending node; finding a next hop to forward the RESOLVE message;modifying the RESOLVE message to indicate processing the RESOLVEmessage; and forwarding the RESOLVE message to the next hop if the nexthop is verified.
 3. The method of claim 1, wherein the indication thatthe RESOLVE message will not be processed comprises a setAF_REJECT_TOO_BUSY field.
 4. A computer-readable storage medium havingcomputer-executable instructions for inhibiting denial of serviceattacks based on consumption of processor capacity at a node in apeer-to-peer network, the computer-executable instructions comprisinginstructions for: receiving a potentially malicious message at the nodein the peer-to-peer network; wherein the potentially malicious messagecomprises a RESOLVE message, the RESOLVE message comprising at least onemessage field; examining processor capacity at the node; rejectingprocessing of the potentially malicious message when examining theprocessor capacity at the node indicates that the consumption ofprocessor capacity at the node is above a predetermined level, whereinrejecting processing of the potentially malicious message comprisessending an AUTHORITY message, the AUTHORITY message containing anindication that the potentially malicious message will not be processedbecause the consumption of processor capacity at the node is above thepredetermined level; and accepting processing of the RESOLVE messagewhen examining the processor capacity at the node indicates that theconsumption of processor capacity at the node is below the predeterminedlevel.
 5. The computer-readable storage medium of claim 4, wherein theindication that the RESOLVE message will not be processed comprises aset AF_REJ ECT_TOO_BUSY field.
 6. The computer-readable storage mediumof claim 4, further comprising: processing the RESOLVE message;converting the RESOLVE message to a RESPOND message when another nodeidentification is locally registered at the node; and sending theRESPOND message to the other node.
 7. The computer-readable storagemedium of claim 4, further comprising: processing the RESOLVE message atthe node; calculating a bitpos as a hash of the at least one messagefield when a second node identification is not locally registered;setting a first bit at an index of a bit vector, the index of the bitvector corresponding to the bitpos; storing the bit vector at the node,the bit vector specifically identifying the RESOLVE message with thesecond node; finding a next hop to forward the RESOLVE message;modifying the RESOLVE message to indicate processing the RESOLVEmessage; and forwarding the RESOLVE message to the next hop if the nexthop is verified.
 8. The computer-readable storage medium of claim 7,further comprising: setting a second bit in the RESOLVE message when thenext hop is not verified; and forwarding the RESOLVE message to the nexthop; wherein the second bit comprises a request to identify theownership of the RESOLVE message.
 9. A method of inhibiting denial ofservice attacks based on consumption of processor capacity at a node ina peer-to-peer network, comprising: receiving a potentially maliciousmessage at the node in the peer-to-peer network; wherein the message isa FLOOD message, the FLOOD message containing a peer address certificate(PAC); determining that the PAC should be stored in a cache at the node;examining processor capacity at the node; and rejecting processing ofthe potentially malicious message when examining the processor capacityat the node indicates that the consumption of processor capacity at thenode is above a predetermined level, wherein rejecting processing of thepotentially malicious message comprises sending an AUTHORITY message,the AUTHORITY message containing an indication that the potentiallymalicious message will not be processed because the consumption ofprocessor capacity at the node is above the predetermined level.
 10. Themethod of claim 9, wherein receiving a message at the node in thepeer-to-peer network further comprises: determining that the PAC shouldbe stored in one of two lowest cache levels at the node; whereinrejecting processing of the message when examining the processorcapacity at the node indicates that the consumption of processorcapacity at the node is above the predetermined level comprises placingthe PAC in a node set aside list for later processing.
 11. The method ofclaim 10, further comprising processing the PAC in the node set asidelist at a random interval, if, during the random interval, theconsumption of processor capacity at the node is below the predeterminedlevel.
 12. The method of claim 9, wherein receiving the message at thenode in the peer-to-peer network further comprises determining that thePAC should be stored in a node cache level higher than two lowest cachelevels at the node, and wherein rejecting processing of the message whenexamining the processor capacity at the node indicates that theconsumption of processor capacity at the node is above the predeterminedlevel comprises rejecting the FLOOD message.